Mitral valve regurgitation is a common cardiac valve disorder that can be caused by a primary valvular problem (such as damaged valve leaflets) or functional problems that impair leaflet coaptation. A common cause of functional mitral valve regurgitation is dilated cardiomyopathy caused by myocardial infarction, chronic myocardial ischemia, hypertension, myocarditis, or other causes of heart muscle injury. Enlargement of the mitral annulus and left ventricular cavity produce mitral valvular insufficiency that can cause volume overload that further exacerbates the underlying myopathy and worsens the valvular insufficiency. Mitral valve repair can reduce mitral regurgitation and correct secondary mitral annular dilation to thereby improve mitral valve leaflet coaptation. One such repair technique is an annuloplasty procedure, in which the annulus of the valve is surgically reconstructed or augmented by placement of a ring around the valve annulus to reduce its circumferential and septal-lateral dimensions. In patients with congestive heart failure and secondary mitral regurgitation, annuloplasty can provide a long-term symptomatic and survival benefit.
Traditional mitral valve annuloplasty requires open heart surgery with a sternotomy or thoracotomy and cardiac arrest and cardio-pulmonary bypass. For example, the annuloplasty procedure is performed through a surgical incision in which the effective size of the valve annulus is reduced by attaching a prosthetic annuloplasty ring to the left atrial aspect of the mitral valve annulus. A variety of rigid and flexible annuloplasty rings have been developed for this purpose, such as those shown in U.S. Pat. Nos. 4,917,698; 5,041,130; 5,061,277; 5,064,431; 5,104,407; 5,201,880; and 5,350,420. Although very effective, this open-heart procedure is accompanied by substantial morbidity and prolonged convalescence. As a result, the procedure often is not offered to patients who are insufficiently symptomatic to justify the surgical risk and morbidity, or to patients who suffer advanced disease, or to patients with substantial co-morbidity.
Percutaneous approaches to mitral valve repair have been developed to reduce the clinical disadvantages of the open-heart procedures. In some percutaneous techniques, a prosthesis is advanced in a catheter through the subject's vasculature to the vicinity of the mitral valve. These percutaneous techniques are attractive alternatives to conventional surgical treatment because they do not require open heart surgery or extracorporeal circulation, and they can be used in a closed and beating heart. The treatment is potentially less morbid and can be applied to a wider range of patients including those with less severe valvular dysfunction.
Examples of percutaneous mitral valve repair procedures include coronary-sinus shortening devices, transcameral fixtures, endoventricular annular plication, and direct leaflet stapling. Coronary sinus annuloplasty techniques have been disclosed, for example, in U.S. Pat. Nos. 6,402,781 and 7,090,695, as well as U.S. Patent Publication Nos. 2004/0254600; 2005/0027351; and 2007/0073391. Some trans-sinus approaches aim to improve mitral valve coaptation by introducing a prosthesis into the coronary sinus to exert forces that reduce the circumference of the posterior mitral annulus or move the posterior annulus toward the anterior leaflet. Coronary sinus methods take advantage of the proximity of the coronary sinus to the mitral valve annulus, such that the pressure of the prosthesis in the coronary sinus pushes the fibrous annulus or the nearby atrial wall inward to reduce the diameter of the annulus.
However, these techniques have shown only limited success in establishing circumferential tension that characterizes effective surgical ring annuloplasty. The sinus-shortening devices have induced only local shortening across the mitral commissures but do not adequately reduce the septal-lateral separation that characterizes functional mitral valve regurgitation. The leaflet procedures have not been able to reduce annular dilation and they can also impair the normal dynamic line of mitral valve coaptation that accommodates a range of volumes and inotropic states.
A more recent improvement of percutaneous annuloplasty is coronary sinus transcatheter-mitral-valve cerclage annuloplasty in which a tensioning material is placed around the mitral valve annulus using a catheter, such as a steerable guide wire or cannulation catheter. Certain cerclage trajectories can compensate for coronary sinus anatomy that is remote from the mitral valve annulus, by rotating the plane of circumferential tension toward the left ventricular outflow tract. In cerclage, a continuous strand of tensioning material (such as suture material) is applied along a pathway that extends at least partially through the coronary sinus and then reenters the right side of the heart, for example by passing through a basal septal perforator vein and penetrating a small distance through septal myocardium. The tensioning material is placed with the assistance of imaging technologies that may include X-ray fluoroscopy, magnetic resonance imaging, intracavitary or external ultrasound, electroanatomic mapping, X-ray computed tomography or a combination (fusion) of any of these imaging technologies.